The six-month amnesty for banned firearms does not cover their use, and those who try may face the full force of the law, police say.
And they admit they have no idea how many semi-automatics are currently in New Zealand, and it could be well into the tens of thousands.
Police Deputy Commissioner Mike Clement held a press conference this morning to show the types of firearms that will no longer be legal under the new gun law, which passed through Parliament last night and will come into force tomorrow.
An amnesty until the end of September, which the Government can extend, means that people with prohibited firearms will not be prosecuted if they are found with their firearms or surrender them to police.
But that did not mean they could use them during the grace period, Clement said.
"If they do find themselves unable to resist the urge, then we'll take each case as it comes.
"The amnesty provisions protect licence holders with good intent ... Those people who threaten or actually harm others with firearms can expect police to act swiftly in accordance with existing firearms legislation."
Clement urged firearms owners to register prohibited firearms with police through the website or by ringing 0800 311 311.
"I urge gun owners to register online, be patient, keep the firearms secure, so by the time police is ready to receive those firearms, we can do so safely."
He said it was likely police would go into communities to collect firearms, rather than have queues of people with guns lining up outside police stations.
Police were also building the capacity to safely store surrendered weapons, which will eventually be destroyed.
There are about 13,500 firearms under an E-Category licence, which will all be illegal from tomorrow. But there are no records of the number of A-Category firearms that will be illegal.
"It could be in the tens of thousands. It could be more. There is no register of the firearms fleet in New Zealand for Category A firearms ... I do not know the size of that fleet," Clement said.
"I expect 100 per cent compliance. I keep being told by the firearms community that these are law-abiding, fit and proper people. Through no fault of their own, the legislation has changed and they want to continue to be law-aiding citizens.
"I'm not going to stand in front of you and say 80 per cent is good enough. We are going to push hard to make sure we reach every gun licence holder and make it very clear to them about what the expectation is under this new legislation."
Clement said police would also talk to gangs, if they are open to it, which have said they will not hand in their guns.
"We're open to any approach from anybody in any part of our community with regard to those who want to surrender firearms, legal or illegal.
"We all know there are firearms in the hands of people who should just not have them and who use them unlawfully. That's true today, and it will be true tomorrow when the legislation comes into place.
"We all have to be real about this. Some have stated there are going to be those out in the community who have no intention of surrendering illegal firearms."
Police were criticised during the select committee process last week for their poor handling of firearms control.
Clement acknowledged that police engagement with the firearms community has not been good enough.
"Has it been good enough? Some will say 'no'. Quite frankly, I can stand in front of you and say 'no'.
"The reality is we have to be exemplary with regard to this. This is all about making New Zealanders safer and free of semi-automatic firearms."
Changing firearms laws amend the Arms Act by:
• Banning most semi-automatic firearms and some pump-action shotguns; and also certain large-capacity magazines. There are limited exemptions.
• Placing controls around who may possess parts of prohibited firearms.
There will no longer be a category of firearm known as a military style semi-automatic firearm (or MSSA) and the old "E" endorsement will be obsolete.
The newly banned items will be called prohibited firearms, prohibited magazines, and prohibited parts. New offences involving prohibited items carry tougher penalties.
Transitional provisions allow for an amnesty until six months after the buyback is announced so that those in possession of prohibited items have time to notify police and can hand over their firearm/s to police at a later stage when we advise of that process.
Prohibited firearms are:
• All semi-automatic firearms (including semi-automatic shotguns), but:
• excluding rimfire rifles .22 calibre or less as long as they have a magazine (whether detachable or not ) that holds 10 rounds or less; and
• excluding semi-automatic shotguns that have a non-detachable, tubular magazine that holds five rounds or less.
Pump action shotguns that:
• Are capable of being used with a detachable magazine; or
• Have a non-detachable tubular magazine capable of holding more than five cartridges.
Only a person who meets one of the exemption categories and who has applied for and obtained a new endorsement and permit to possess may lawfully possess a prohibited firearm.
Prohibited magazines are:
• Shotgun magazines (whether detachable or not) capable of holding more than five rounds
• Magazines for other firearms (excluding pistols) that are:
• Detachable magazines capable of holding more than 10 rounds and that are capable of holding 0.22 calibre or lower rimfire cartridges
• Detachable magazines capable of holding more than 10 rounds and that are capable of being used with a semi-automatic or fully automatic firearm
• Other magazines, detachable or not, that are capable of holding more than 10 rounds.
Only a person who meets one of the exemption categories and who has applied for and obtained a new endorsement and permit to possess may lawfully possess a prohibited magazine.
Prohibited parts are:
• Parts of prohibited firearms; and
• Components that can be used to make a firearm fire with (or near to) semi-automatic or automatic action.
Only a person who has an endorsement permitting them to possess a prohibited firearm may lawfully possess a prohibited part.